Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $93.74   11.600%   $104.6138   $104.61   $104.60   $104.60  
  Purchase #2 $178.86   13.623%   $203.2261   $203.23   $203.25   $203.20  
  Purchase #3 $224.58   11.427%   $250.2428   $250.24   $250.25   $250.20  
  Purchase #4 $79.91   10.705%   $88.4644   $88.46   $88.45   $88.50  
  Purchase #5 $155.42   7.748%   $167.4619   $167.46   $167.45   $167.50  
  Purchase #6 $129.65   8.441%   $140.5938   $140.59   $140.60   $140.60  
  Purchase #7 $26.27   10.377%   $28.996   $29.00   $29.00   $29.00  
  7 purchase totals = $888.43       $983.5988   $983.59   $983.60   $983.60